1. Field of the Invention
The present invention relates to a printed circuit board, and, more particularly, to electroconductive paste to be enclosed in a through hole connecting circuits disposed on the two sides of a printed circuit board.
2. Description of the Related Art
Hitherto, double-side printed circuit boards have been designed in such a manner that predetermined patterns of electroconductive bodies are formed by two sheets of copper foil laminated on the two sides of an insulating substrate of a copper laminated board, through holes being formed at predetermined positions in the substrate, and electroconductive paste which is normally made of copper paste being enclosed in predetermined through holes so that electrical connection between two circuits on the two sides of the insulating substrate is established.
The other manufacturing processes such as mounting of the electronic parts, soldering, and forming insulating coating are performed in known ways. Thus detailed description of these factors will be omitted here.
There has, however, been a demand for the size of such printed circuit boards to be reduced in accordance with the trend for reducing the size of electronic parts. Furthermore, in order to reduce the number of manufacturing processes, a significant degree of automation has been achieved. This raises the problem that when a copper paste is introduced from one side into the through holes by means of silk screen printing, the copper paste cannot be properly adhered to the conductive body of the circuit disposed on the reverse side, leading to a condition of defective conduction.
If an excessive amount of copper paste is supplied on the silk screen when silk screen printing with copper paste is performed, the copper paste overflows the target regions, causing short circuits or the like between the circuits on the two sides. There is, therefore, a certain limitation to the amount of paste that can be supplied on the silk screen, but this restricted amount of paste is insufficient to overcome the problem of defective conduction.
To this end, an object of the present invention is to provide a printed circuit board capable of overcoming the above-described problems and of displaying a high level of reliability and in which the generation of defective conduction can be prevented without comprising the conventionally achieved level of facility for manufacture and maximized economic advantage.